1. Field of the Invention
The present invention relates to the processing of video signals for a color video camera.
2. Description of Related Art
FIG. 1 is a block diagram of a prior art video signal processor. In FIG. 1, the reference numeral 1 designates an R-Y color-difference signal input terminal, 2 is a B-Y color-difference signal input terminal, 3 is a luminance signal input terminal, 4 is an aperture correction signal input terminal, 5 is an R-Y color-difference signal output terminal, 6 is a B-Y color-difference signal output terminal, 7 is a luminance signal output terminal, 8 is an aperture correction signal output terminal, 9 through 12 refer to control signal input terminals, and 13 through 16 denote gain controllers.
Next, the operation of the video signal processor will be described below. Color-difference signals applied to the R-Y color-difference signal input terminal 1 and the B-Y color-difference signal input terminal 2 are transferred to the gain controllers 13 and 14, respectively, where the gains of the signals are controlled in accordance with control signals D1 and D2 for proper color reproduction before being output at the R-Y color-difference signal output terminal 5 and the B-Y color-difference signal output terminal 6, respectively. On the other hand, the luminance signal applied to the luminance signal input terminal 3 is transferred to the gain controller 15, where the gain of the signal is controlled in accordance with a control signal D3 before being output at the luminance signal output terminal 7. The aperture correction signal applied to the aperture correction signal input terminal 4 is transferred to the gain controller 18, where the gain of the signal is controlled in accordance with a control signal D4 before being output at the aperture correction signal output terminal 8.
FIG. 2 is a block diagram showing another prior art video signal processor. In FIG. 2, the same reference numerals as those in FIG. 1 designate the same or corresponding parts, while the numerals 17 and 18 designate operational circuits.
Now, the operation of this video signal processor will be described below. An R-Y color-difference signal applied to the R-Y color-difference input terminal 1 is transferred to the operational circuit 17 as well as to the gain controller 14, and a B-Y color-difference signal applied to the B-Y color-difference signal input terminal 2 is transferred to the operational circuit 18 as well as to the gain controller 13. In the gain controllers 13 and 14, the gains of the color-difference signals are controlled in accordance with control signals D5 and D6 for proper color reproduction. The output of the gain controller 13 is supplied to the operational circuit 17, while the output of the gain controller 14 is supplied to the operational circuit 18. The operational circuits 17 and 18 add the two input signals and output the respective sum signals at the R-Y color-difference signal output terminal 5 and the B-Y color-difference output terminal 6.
One problem with the above configured prior art video signal processors has been that flesh tones cannot be corrected without affecting the tones of other colors, since the gains of the color-difference signals can only be varied in the directions along the R-Y and B-Y axes.
Another problem with the prior art has been that it is extremely difficult to vary the gain of the luminance signal and the gain and frequency characteristic of the aperture correction signal selectively for flesh-tone areas.
The prior art has a further problem that, when the lighting is not used and proper makeup is not done on the face of the object person, the luminance on the human face is not sufficient and wrinkles on the human face become emphasized because of camera signal processing such as .gamma.-correction.
FIG. 3 is a block diagram of still another prior art signal processor for a color video camera In FIG. 3, the reference numeral 21 is a focus lens, 22 is a solid state imager, 23 is a co-related double sampling (CDS) circuit, 24 is an automatic gain controller (AGC), 25 is an A/D converter, 26 is a signal processor, 27 is a window pulse generator, 28 is a data selector, 29 is a band-pass filter (BPF), 30 is an integrator, 31 is a microcomputer, 32 is a motor drive circuit for driving a motor 33, 33 is the motor for moving the focus lens 21, 34 is a luminance signal output terminal, 35 is an R-Y color-difference signal output terminal, 36 is a B-Y color-difference signal output terminal, 37 is a data selector, 38 is an integrator, 39 is an iris, 40 is a motor for moving the iris 39, 41 is a motor drive circuit for driving the motor 40, 42 is a timing generator (TG) for driving the solid state imager, 43 is a solid state imager drive circuit, 44 is a zoom lens, 45 is a motor for moving the zoom lens 44, 46 is a motor drive circuit for driving the motor 45, 47 is a data selector, 48 is an integrator, and 380 is an A/D converter.
The operation of this video signal processor will be described below. An optical image, focused through the zoom lens 44 and focus lens 21, is converted by the solid state imager 22 into an electrical signal. The TG 42 outputs imager reading pulses which are supplied to the solid state imager drive circuit 43 and in synchronism with which a video signal is output from the solid state imager 22. The CDS circuit 23 only extracts signal components from the output signal of the solid state imager 22 which is mixed with noises, and after the gain of the output signal of the CDS circuit 23 is controlled by the AGC 24, the signal processor 26 performs signal processing such as color separation and matrixing on the output signal to produce the luminance signal, R-Y color-difference signal, and B-Y color-difference signal.
The data selector 37 selects a part of the video signal which lies inside a picture frame determined by the window pulse generator 27. The video signal selected by the data selector 37 is integrated by the integrator 38 for every vertical scanning period. In accordance with an output signal supplied from the integrator 38, the motor drive circuit 41 controls the opening of the iris 39 by means of the motor 40.
The data selector 47 selects data that lie inside the picture frame determined by the window pulse generator 27. The video signal selected by the data selector 47 is integrated by the integrator 48 for every field period. In accordance with an output signal supplied from the integrator 48, the gain in the AGC 24 is controlled so that the output signal of the AGC 24 is maintained at a constant level. The output signal supplied from the integrator 38 is digitized by the A/D converter 380. Then, in accordance with an output digital signal supplied from the A/D converter 380, the microcomputer 31 outputs a control signal to the timing generator 42 to control the speed of an automatic electronic shutter.
The data selector 28 selects a part of the video signal which lies inside the picture frame determined by the window pulse generator 27. The video signal selected by the data selector 28 is passed through the band-pass filter 29 to extract the frequency components necessary for auto focusing, and the extracted frequency components are integrated by the integrator 30 for each vertical scanning period. The output signal of the integrator 30 is fed to the microcomputer 31 to control the motor drive circuit 32. That is, the microcomputer 31 supplies a control signal to the focus lens drive circuit 82 which controls the focus lens 21 by means of the motor 33. On the other hand, the motor drive circuit 46 controls the motor 48 to vary the magnifying ratio for the object.
The prior art video signal processor of the above construction has a problem that the light from a main object (person) cannot be accurately measured when the object is at backlight, thus causing a so-called phenomenon of "black compression", i.e., loss of grayscale in the low luminance portions of the video signal. It also has a problem that the light from a main object (person) cannot be accurately measured when the object is illuminated with excessive front lighting, thus causing a so-called phenomenon of "white saturation", i.e., saturation of the high luminance portions of the video signal. Furthermore, the prior art has a problem that, since the center of the video signal area is taken as the primary focus area, correct focusing cannot be achieved when a main object (person) is not positioned in the center area or is located outside the focus area. The prior art has a further problem that, since the center of the picture area is taken as the primary photometric area, iris control, automatic gain control, and automatic electronic shutter speed adjustment cannot be done properly for a main object (person).
FIG. 4 is a block diagram of a color video camera capable of videotaping the camera operator himself by remote control, and FIG. 5 is a schematic diagram showing the camera operator video taping himself. In FIG. 4, like or corresponding parts to those in FIG. 3 are designated by like reference numerals. In FIG. 4, the reference numeral 49 designates a remote controller, and 50 a receiving circuit. In FIG. 5, 51 is the operator videotaping himself by remote control, 52 is a video camera, and 53 is a tripod for supporting the video camera 52 in position. The remote controller 49 transmits recording function control signals such as "recording instruction", "recording stop instruction", etc. Acoustic or electric waves, or light may be used to transmit such control signals from the remote controller 49 to the color video camera 52. In the example hereinafter described, light such as infrared light is used. The receiving circuit 50 receives a light pattern of an infrared signal transmitted from the remote controller 49 and transfers the received signal to the microcomputer 31. The microcomputer 31 outputs a control signal to initiate the recording of video signals when a "recording instruction" is given, and a control signal to stop the recording of video signals when a "recording stop instruction" is given.
The prior art color video camera of the above construction has a problem that, when videotaping himself by remote control, the operator needs to check through a monitor, such as a viewfinder of the video camera, to determine whether he is positioned inside the picture frame. There has also been a problem that, while the operator is being videotaped for recording by remote control, there is a possibility that the object (the operator) may move outside the picture angle of the video camera without the operator knowing of it. The prior art has a further problem that, while the operator is being videotaped for recording by remote control, the operator's face may not be held within the picture frame and the operator himself may not be positioned properly in the center unless he checks the monitor for the picture being recorded.
It is also known that an image superimposing device called a chromakey device is used when superimposing an object image taken by a color video camera on a prescribed background image such as a landscape picture. Using the chromakey device, an object image to be fitted in is recorded against a background of a specific hue; the resulting video signal is compared with this specific hue to distinguish the portions of the signal that do not coincide with the specific hue, and a keying signal is generated in order to output only those portions that do not coincide with the specific hue, i.e. the video signal portions that lie within the area of the object image.
FIG. 6 is a block diagram showing the constitution of a prior art image superimposing device, for example, described on pp.116-119 in "Image Electronics Seminar 8, Image Software," Corona-Sha, pp.116-119, Aug. 30, 1980. In FIG. 6, the reference numeral 54 is a lens, 55 is an image sensor, 56 is a processing circuit, 57 is an encoder circuit, 58 is a synchronizing circuit, 59 is a NOT circuit, 60 and 61 are gate circuits, 62 is a superimposing circuit, 63 and 64 are buffer amplifiers, 65 and 66 are differential amplifiers, 67 and 68 are slice circuits, 69 is a reference R-Y color-difference signal input terminal, 70 is a reference B-Y color-difference signal input terminal, 71 and 72 are variable resistances, 73 and 74 are level converters, and 75 is an AND circuit.
Next, the operation of this image superimposing device will be described below. First, an object image to be fitted in is recorded against a background of a specific hue. The optical image of the object is focused through the lens 54 onto the image sensor 55 for conversion into an electrical signal corresponding to the brightness of the optical image. The electrical signal is supplied to the processing circuit 56 which processes this signal to produce a Y signal, an R-Y color-difference signal, and a B-Y color-difference signal. These signals are converted by the encoder circuit 57 into a video signal for recording.
The R-Y color-difference signal and B-Y color-difference signal are also supplied to the buffer amplifiers 63 and 64, respectively, for impedance conversion. These signals are then fed to the differential amplifiers 65 and 66 where the levels of these signals are compared with the levels of the respective reference color-difference signals of the background color, the results then being supplied to the slice circuits 67 and 68. In the slice circuits 67 and 68, the input signals are sliced at the slice levels set by the variable resistances 71 and 72. The specific hue of the background is set through the reference R-Y color-difference signal input terminal 69 and reference B-Y color-difference signal input terminal 70; since a man is usually selected as the object, blue, a complementary color of flesh color, is selected as the specific hue. When the obtained color-difference signals coincide with the specific hue, the outputs of the slice circuits 67 and 68 remain nearly unchanged, and when they differ from the specific hue, there occur significant variations in the outputs of the slice circuits 67 and 68. The level converters 73 and 74 output a binary logic level, either "0" or "1", to correspond to the outputs of the slice circuit 67 and 68. FIG. 7 is a diagram illustrating the operation described above, in which an output from the differential amplifier 65, an output from the slice circuit 67, and an output from the level converter 73 are shown by way of example when an object 77 in a picture 76 is taken along line A-B. The outputs of the level converters 73 and 74 are ANDed by the AND circuit 75 to produce a keying signal.
Synchronized with the video signal, a background image signal is supplied to the gate circuit 61 from the synchronizing circuit 58. In response to the keying signal supplied from the AND circuit 75, the gate circuit 60 extracts the components corresponding to the area of the object from the video signal supplied from the encoder circuit 57, and the extracted signal is fed to the superimposing circuit 62. On the other hand, the keying signal is inverted through the NOT circuit 59 and supplied to the gate circuit 61 which extracts the components corresponding to the background area from the background image signal supplied from the synchronizing circuit 58, and the extracted signal is fed to the superimposing circuit 62. The superimposing circuit 62 superimposes the outputs of the gate circuits 60 and 61 to produce a superimposed video image.
The prior art image superimposing device of the above construction has had the various problems described below. First, a color greatly different in hue from the color of the object has to be selected as the background color for distinct separation between the object and the background. For example, when the object is a human, a complementary color of flesh color, i.e. blue, is usually selected as the background color, which requires a blue background called a blue back. It is also required that the color of the object placed against the background should be greatly different in hue from the background color. Therefore, when blue is selected as the background color, purple or greenish blue colors containing a high degree of blue components cannot be used as the color of the object because of their difficulty of separation from the background color. This has caused such a problem as limiting the selection of clothes that the human can wear. Furthermore, when a plain-colored curtain is selected as the background and the luminance of the background color varies because of variations in the luminance by the pleats in the curtain, separation between the background and the object placed against the background becomes unstable. Further, the reference blue back is not always available as the background. For example, in an ordinary home situation, a wall that is not blue in color may often be used as the background against which an object is recorded. In such a case, the wall color must be set as the background color, but changing the background color requires adjustment of the reference levels and slice levels and these levels must be individually adjusted for variations in the reference background color or camera characteristics. In an ordinary home, it is also difficult to prepare a background of uniform luminance and hue; for example, when setting the background color with a wall, curtain, etc. as the background, the adjustments become even more difficult as stains, creases, etc. on the background cause variations in the luminance and hue, which leads to unstable separation between the background and the object placed against the background. Furthermore, the image superimposing device generally requires using a camera for creating the keying signal and an external camera or a video tape recorder (VTR) for producing a background picture and also requires maintaining synchronization between these devices. The problem is that the construction of the device is made bulky as a result.